Glass is almost infinitely selective in separations involving either hydrogen or helium. In addition, glass spheres have been proposed as a means for storing hydrogen. The extremely low permeability of hydrogen through glass at ambient temperatures provides a basis for using glass microspheres as a medium for hydrogen storage and separation devices. A disadvantage associated with these devices is that the glass has insufficient permeability for rapid release of the gas. This lack of permeability affects devices employing glass microspheres by requiring enormous surface areas for rapidly loading and unloading hydrogen.
Designers have attempted to solve this problem by using temperature to control the permeability of hydrogen or helium through the glass. These processes require temperatures in excess of 300.degree. C. to increase the permeability of hydrogen or helium sufficiently for satisfying the requirements of commercial applications. Unfortunately, the costs associated with the energy and the energy management systems required to adjust permeability are unacceptable for commercial applications. In addition, the slow response or lag time associated with the temperature change does not lend itself to a market where users are accustomed to just turning a valve to receive products.
For example, Robert J. Teitel, in U.S. Pat. No. 4,302,217 "Hydrogen Supply System", describes the use of glass microspheres to store hydrogen. Applying heat to the glass microspheres increases the permeability of the glass to release hydrogen from storage. The released hydrogen then serves as a clean-burning fuel for automobiles. Similarly, Hammel, et. al. in U.S. Pat. No. 4,842,620 "Process of Gas Enrichment with Porous Siliceous-Containing Material," describe the use of hollow glass fibers having pore sizes ranging from 1 to 50 Angstroms in diameter as a device for performing gas separations. This device relies upon the one-way diffusion of gas through glass fibers to enrich gas streams.
As far as known, the low permeability of gases through glass has prevented glass spheres from achieving commercial acceptance for gas storage applications. Furthermore, the lag time associated with releasing hydrogen from glass microspheres prohibits their use for applications that demand an immediate supply of gas. Finally, gas separation applications require enormous lengths of fiber to separate commercial quantities of gas.
It is an object of the invention to provide a cost effective alternative to current commercial methods for storage and transport of gases such as hydrogen that rely on high pressure tanks or use of its liquid phase.
It is a further object of the invention to provide a low-cost selective membrane for separating gases.